Red Stele (Red Core)

Phytophthora fragariae is a soil-borne water mold, not a true fungus, though it behaves similarly in waterlogged conditions. It thrives when soils stay saturated at temperatures between roughly 40°F and 65°F, making cool, wet springs the period of highest risk for established strawberry plantings. Zoospores require free water to move through soil, so drainage is not a minor detail but the primary mechanism that breaks or sustains the disease cycle. Spores persist in infected ground for many years, which is why beds with a documented history of red stele remain hazardous long after the original plants are removed.

The pathogen attacks roots before symptoms appear aboveground. By the time plants show stunting, bluish-green leaf discoloration, few runners, or collapse during fruiting, root damage is already extensive. Splitting a main root lengthwise and finding a red or reddish-brown core confirms the diagnosis. Healthy strawberry roots split to show white tissue throughout.

The most cost-effective management combines two non-negotiable steps: start with certified disease-free planting stock, and select resistant varieties. Earliglow, Allstar, and Sparkle carry documented resistance and perform reliably across a wide range of production systems. Resistant varieties do not eradicate the pathogen from soil, but they substantially reduce plant losses in infected ground. For sites already known to be infected, a minimum 8-year rotation away from strawberries is the standard recommendation before replanting susceptible cultivars. Raised beds or ground with natural slope and rapid drainage reduce infection pressure even when the pathogen is present, because waterlogged conditions rarely develop long enough to allow zoospore movement.